Process for toughening and hardening taps for cutting screw threads, milling cutters, and other cutting tools



Patented Feb. l2, 1929. 1,570

eniren STATES PATENT OFFICE.

REGINALD LEIRJ-LIYI'IB m KhlIGIlLT AND FREDERICIhLYIlIOI-I, (3F BURNHAM, ENGLAND.

LEROGESS FOR TOUGHENING AND HARDENING TAPE FOR CUTTING SCREW THREADS, MILLING GUTTERS, AND OTHER CUTTING TGULS.

N Drawing. Application filed August 25, 1927, Serial N 0. 215,528, and in Great Britain September 1, 1928.

This invention relates to a process for of the tap or toolis thus heated to a degree toughening and hardening taps for cutting necessary to restore the centre of said tap or 45 threads in met-ah milling cutters and other tool, only, to its original soft condition. cutting tools, and has for its object to produce Preferably the heating element usedfor the a tap or tool whose core is tougher than its purpose is an electric element which may con outer cutting portion, thus giving increased slstoii one or more heating wires through strength and minimizing the tendency to which electric current is passed, said wire or 50 :t'racture due to stresses imposed when the tap wires residing in and projecting from each or tool is in use, and to eii'ect the said toughend of the top or tool. The electrical conening without affecting substantially the motions with the wire or wires to permit hard condition of the outer cutting portion. the engagement and disengagement oi"- the According to the invention, the toughening top or tool with said. Wire or wires may be of 55 f the, core of th ta or tool is ff t d by any'suitable form and do not concern the heating; said core after the tap or tool has present invention.

been bodily hardened, thus softening the said By the above-described process the core of core whilst leaving the outer cutting portion the top or tool is toughened whilst leaving the of the tap or tool in hard condition. cutting edge of the tool hard. so

in carrying out the said invention, a tap Various modifications may be made in the for cutting; a. screw thread a milling cutter process above-described without departing or other cutting tool is made in the usual from, the scope of the invention. For inmanner up to the final operationbefore hardstance, the clay or similar filling material for insertion in the hole prior to hardening. need c5 B r id t ()1' tool i hard ned h l not necessarily be used; and, further, instead pyeportionate i diameter to the, size of the of forming a hole completely through the tap tap or tool is drilled along the longitudinal or tool for accommodating the heating elecentre line of the tap or tool so as to open out went, a cavity with only one open end may at each end oi? said tap or tool. As an exarnbe formed in said tsp for accommodating said pic Oil the size of hole formed in a screw top heating element. it is convenient in the case of a tap intended We claim 30 ior threading a half-inch diameter hole, to A process for toughening and hardening make a one-eighth inch diameter hole taps for cutting screw threads. consisting in through said tap. hollowing' out said top, whilst in its soft The hole thus formed in the tap or tool state, introducing a filling; i'naterial into said is then filled with clay or other suitable filling hollow and then hardening the tap bodily,

and the tap or tool is bodily hardened in the and finally softening the core of the tap by well-known manner, the said filling ensuring heating the interior thereof to toughen the even heat throughout the tap or tool during same.

the hardening process and minimizing the In testimony whereof we have atlixed our risk of same distorting when immersed in signatures hereto this 13th day of August.

* liquid during such process. 1927.

After such hardening operation the filling is removed. a heating element is introduced REGINALD FRANK KNIGHT.

into the hole in the tap or tool and the core FREDERICK LYNCH. 

